The Internet Protocol Multimedia Subsystem (IMS) refers to a core network that supports multimedia services based on a future evolution of 3G networks, where there exists only a single core network supporting convergent voice and data services, i.e., multimedia services. The multimedia services are based on Voice over Internet Protocol for signaling and media transport. An IMS core network consists of a variety of standardized functional elements, including, but not limited to, one or more instances of a Call Session Control Function (CSCF), Breakout Gateway Control Function (BGCF), Media Gateway Control Function (MGCF), Home Subscriber Server (HSS), Media Gateways (MGW), and an application server (AS). Signaling within the IMS core network is based on the Session Initiation Protocol (SIP) using any interface compatible with the Internet Protocol (IP). Herein, IMS is defined as the system specified by the Third Generation Partnership Project (3GPP), Third Generation Partnership Project 2 (3GPP2) and European Telecommunications Standards Institute (ETSI) Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN).
Messaging applications, e.g., short message service (SMS), are used extensively in the existing Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) networks and are considered key services for deployment in IMS networks. In order for network operators to maintain a strong competitive position in the telecom industry, upgrades of existing networks and the introduction of new IP multimedia revenue generating services are necessary.